Photoluminescence enhancement and morphological properties of nanoporous anodic alumina prepared in oxalic acid with varying time and temperature

We report on the photoluminescence (PL) enhancement and morphological properties of highly ordered Nanoporous anodic alumina (NAA) fabricated by two-step anodization for 2–10 h at 5 °C and 25 °C anodization temperatures. Structural features and pore arrangements of NAA were characterized. Pore-properties such as pore-diameter, porosity and growth rate showed an increase with rising in temperature whereas pore-wall thickness and barrier layer thickness decreased, however, interpore distance and pore density were not affected. Two-dimensional fast Fourier Transform (FFT) analysis was used to study the pore arrangement. The average pore regularity ratio was higher at 5 °C. The Photoluminescence (PL) spectra of NAA samples exhibited a strong visible blue emission at room temperature. The broad PL peak was deconvoluted into two Gaussian sub-bands attributed to luminescent F⁺ and F centers. Experimental results showed that NAA prepared at elevated temperature showed PL enhancement by about 3.6–4.8 fold due to the increased anodizing current which leads to the increased density of F centers compared to F⁺ centers.